The present invention is directed to a method of removing material from a subsurface and is particularly useful for drilling, well construction, and recovering soil, soil gas, and groundwater samples.
A casing is often used when removing material from a subsurface. The casing seals the borehole, prevents cross-contamination of aquifers and the borehole environment, and prevents the borehole from caving in as drilling progresses. The casing also provides a conduit for well casing, sand, bentonite and cement.
A known technique for casing a borehole is commonly referred to as air rotary casing hammer. A hollow rotary drill pipe having a drill bit at the downhole end is used to cut through the formation. The casing, which surrounds the drill pipe, is driven into the formation using a hammer which pounds the casing into the formation with a number of successive blows. The bottom of the casing has a drive shoe to facilitate penetration of the formation.
Rotary drilling produces cuttings which must be removed for continued drilling. Air or mud is introduced through the interior of the drill pipe as a circulating medium to remove the cuttings. The air or mud flows down the hollow interior of the drill pipe to the bottom of the borehole and circulates back up the borehole in the annular area between the drill pipe and casing. The air or mud and cuttings are then discharged into a hopper for subsequent analysis, treatment and/or disposal.
A problem with air rotary casing hammer is the production of waste products due to the use of a circulating medium and the fact that rotary drilling produces cuttings which must be removed for continued drilling. When operating below the water table, air rotary drilling also brings a substantial amount of water out of the formation which must be disposed of. The fluid and cuttings must be stored, tested, treated, and disposed of in accordance with strict Federal and State regulations when working in a potentially contaminated formation. Transportation, testing, treatment and disposal of the fluid and cuttings significantly increases the cost involved with the drilling, sampling and/or well construction.
Another problem with air rotary casing hammer is that the circulating air can carry contaminated dust and water vapor outside the borehole and into the environment.